The 10 days is to give the original claimant time to respond, but to do that YouTube needs to forward the counter-takedown to the original claimant, which they have refused to do.

> (B) upon receipt of a counter notification described in paragraph (3), promptly provides the person who provided the notification under subsection (c)(1)(C) with a copy of the counter notification, and informs that person that it will replace the removed material or cease disabling access to it in 10 business days; and

https://www.copyright.gov/title17/92chap5.html#512